The present invention concerns a system and method for maintaining a constant throttle deadband for an electronically controlled engine. More specifically, the invention provides a system for maintaining the throttle deadband as engine speed breakpoints are modified.
In most automotive and industrial application the internal combustion engines are electronically controlled. In a typical engine control system, a microprocessor receives data from ambient condition and engine-related sensors. The microprocessor then evaluates this data to determine the amount of fuel provided to each engine cylinder.
A typical system is depicted in the block diagram of FIG. 1. In this system, an engine 10 includes a fueling system 12. The fueling system can be of a variety of known types that are operable to provide a particular air-fuel mixture to the engine cylinders. In a typical automotive engine, the fueling system 12 includes an array of fuel injectors that can be individually modulated to provide varying amounts of fuel to the engine cylinders. Specifically, the fueling system 12 operates in response to control signals 13 generated by a fueling command component 14. The fueling company component 14 is generally a software program resident within an engine control module 15. The engine control module 15 receives an engine speed signal 17 from an engine speed sensor 18 affiliated with the engine 10. This speed signal 17 is provided to the fueling command component. In addition, the ECM 15 includes a commanded throttle control component 20. The commanded throttle control component. 20 receives an input signal 22 from a throttle position sensor 24. The position sensor 24 determines an operator requested position of input, such as throttle pedal 25, as it is manipulated by the driver of the vehicle. Typically, the throttle position sensor 24 provides a position signal 22 voltage that is a direct measure of the angle of the throttle pedal 25. The control component 20 then translates that voltage to a magnitude signal or commanded throttle valve.
The fueling command component 14 receives the engine speed signal 17 and a commanded throttle value generated by the component 20. The fueling command component of the ECM then evaluates this input in light of pre-programmed fueling protocols to generate an appropriate fueling command signal 13 for the fueling system 12.
In a typical internal combustion engine, the greater that the pedal 25 is depressed, the greater the amount of fuel provided to the engine 10 by the fueling system 12. In a simple system, the resulting engine speed is linearly related to the position of the throttle pedal 25, as reflected in the graph of FIG. 2. When the pedal 25 is at its neutral, or zero throttle position, the engine is operating at its minimum or low idle speed. When the throttle pedal 25 is fully depressed, or at its maximum position, the engine speed is also at its maximum rpm value. It is understood that FIG. 2 is simply an idealized representation of the relationship between throttle position and engine speed. Of course, other relationships can be implemented in many types of engine control systems. Typically, an algorithm or a table-look-up procedure is utilized to extract a fueling command based upon the sensed position of the vehicle throttle.
In many engine control systems, an engine speed breakpoint (BP) is provided or monitored by the engine control module 15. This breakpoint corresponds to an established maximum permitted engine speed that is less than the unregulated maximum engine speed at the maximum throttle position. The breakpoint can be correlated to an engine speed control in that the engine speed will not increase beyond the breakpoint regardless of how far the throttle pedal 25 is depressed. By way of example, referring again to FIG. 2, two throttle breakpoints BP.sub.1 and BP.sub.2 are depicted. These two breakpoints can be preset by the engine manufacturer, or in a more typical situation, can be established by the vehicle operator. As illustrated in FIG. 2, as the vehicle throttle is depressed from its zero position, the relationship between the throttle position and engine speed follows the standard curve C.sub.0 (which follows a linear relationship in the specific embodiment.) `However, when the engine speed reaches one of the breakpoint values, either BP.sub.1 or BP.sub.2 any further movement of the throttle does not result in an increase in engine speed. In other words, once the vehicle engine speed has reached a breakpoint value, the fueling command component 14 essentially overrides the commanded throttle component 20 so that the fueling command ignores the throttle position. On the other hand, once the engine speed drops below the breakpoint value, the fueling command routine 14 again determines the fueling command signal 13 as a function of throttle position.
In a typical electronically controlled engine, the portion of the throttle travel that has no effect on engine speed is referred to as the "deadband". In other words, when the throttle is within the deadband, any modulation of the throttle pedal 25 is essentially irrelevant to determining the amount of fuel commanded at the fueling system 12. As can be discerned from FIG. 2, this deadband increases as the breakpoint engine speed decreases. This deadband thus, corresponds to a segment of travel of the throttle pedal 25 that produces no change in engine speed--whether increasing as the pedal is depressed, or decreasing when the pedal is released. FIG. 2 is for illustrative purposes only so that the actual length of the throttle deadband will vary depending upon the particular engine control and throttle system.
A throttle deadband is inherently undesirable because it has a tendency to produce inaccurate or unpredictable engine speed control. This problem is accentuated as the high speed or high idle breakpoint is decreased. When the deadband is increased, the amount of throttle travel between the engine minimum speed (N.sub.min) and the maximum allowable engine speed (i.e., the speed at the breakpoint) is very limited. The vehicle operator thus has less pedal travel to work with to control the engine speed and therefore the vehicle speed, within the engine speed range permitted by the breakpoint. Consequently, when a breakpoint is initiated the throttle pedal becomes a less precise or accurate method for the vehicle operator to control the vehicle speed.
There is therefore a significant need for an engine control system that allows the use of engine speed breakpoints without a commensurate loss in throttle input accuracy. This need extends to the need to eliminate the throttle deadband phenomenon that plagues current engine control systems.